Oil entrainment in vertical refrigerant piping

The aim of this study is to investigate the required refrigerant speed, hen ce minimum refrigeration load, for carrying the lubricating oil up in verti cal sections of refrigerant lines. It is assumed that the downward flow of the thin oil layer over the inner surface of the riser due to gravity is to be balanced with the upward flow of the oil film due to the shear force cr eated by the upward flow of the refrigerant vapor. Velocities are converted to refrigeration capacities by considering a saturated cycle between speci fied condenser and evaporator pressures. General relationships thus develop ed are enumerated for R134a by preparing minimum capacity tables for copper suction and discharge risers. (C) 2000 Elsevier Science Ltd and IIR. All r ights reserved.